Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation Plans (Weighted-Average Assumptions) (Details)

v3.10.0.1
Stock-Based Compensation Plans (Weighted-Average Assumptions) (Details) - $ / shares
12 Months Ended
May 31, 2018
May 31, 2017
May 31, 2016
Performance Stock Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate 2.40%    
Dividend yield 3.30%    
Volatility factor 18.00%    
Expected option life in years 6 years 6 months    
Weighted-average grant-date fair value of stock options granted (per share) $ 7.45    
Stock Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate 2.10% 1.20% 1.90%
Dividend yield 3.40% 3.60% 3.60%
Volatility factor 17.00% 18.00% 18.00%
Expected option life in years 6 years 1 month 6 days 6 years 1 month 6 days 6 years 1 month 6 days
Weighted-average grant-date fair value of stock options granted (per share) $ 6.47 $ 5.74 $ 5.25